1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a reflection type liquid crystal display device that can also function as a transmission type device.
2. Description of Related Art
A liquid crystal display device (LCD) is widely used as a planar display device for a variety of portable computers and portable televisions.
Liquid crystal display devices are classified into two types according to their use of a light source. One type is a transmission type liquid crystal display device, which uses a backlight provided on the back face of a liquid crystal panel as a light source. The other type is a reflection type liquid crystal display device, which uses an external light source such as sunlight or an indoor lamp.
It is difficult to decrease the volume, weight and power consumption of a transmission type LCD because of the presence of the backlight which is used as a light source. For a reflection type liquid crystal display device, the volume, weight and power consumption are low, because the reflection device need not use the backlight. However, if an external environment is dark, the reflection type liquid crystal display device cannot be used.
Accordingly, the present invention is directed to a transmission-reflection type liquid crystal display device that substantially obviates one or more of the problems due to limitations and disadvantages of the related art. In order to overcome the problems of the related art, an object of the present invention is to provide a transmission-reflection type liquid crystal display device which can be driven as a reflection type as well as transmission type. Another object is to provide a transmission-reflection type liquid crystal display device which has good color purity (e.g., calorimetric purity, which is defined by the 1996 Photonics Dictionary as xe2x80x9cRatio, to the luminance of a test color, of the luminance of the spectrum color that matches the test color when mixed with white light.xe2x80x9d).
The transmission-reflection type liquid crystal display device according to the present invention can be driven as a transmission type or reflection type display automatically or by user selection, depending on variations in an external environment. A cholesteric liquid crystal color filter is added to a conventional absorptive color filter and has a high color purity, so that overall color properties of a liquid crystal display device are improved.
In accordance with the purpose of the invention, as embodied and broadly described, in one aspect the invention includes a transmission-reflection type liquid crystal display device, including a first transparent substrate; a second transparent substrate; a liquid crystal layer between the first transparent substrate and the second transparent substrate; a linear polarizer on the second transparent substrate; a cholesteric liquid crystal circular polarizer provided on the first transparent substrate; and a cholesteric liquid crystal color filter provided on the first transparent substrate in order to be situated between the cholesteric liquid crystal circular polarizer and the liquid crystal layer.
In another aspect, the invention includes a liquid crystal display device capable of transmitting light from a backlight and reflecting ambient light, including a lower transparent substrate; an upper transparent substrate; a liquid crystal layer between the lower transparent substrate and the upper transparent substrate; a linear polarizer on the upper transparent substrate; a xcex/4 phase shift plate between the linear polarizer and the liquid crystal layer; and a cholesteric liquid crystal color filter proximate to the lower transparent substrate to selectively reflect ambient light and to transmit light from the backlight.
In another aspect, the invention includes a liquid crystal display device capable of transmitting light from a backlight and reflecting light from a front of the device, including a polarizing layer; a phase shifting layer adjacent to the polarizing layer; a filter layer to selectively reflect light from the front of the device and to transmit light from the backlight; and a liquid crystal layer between the phase shifting layer and the reflecting layer.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.